1. Field of the Invention
The present invention relates generally to a valve timing control system for an internal combustion engine, which control system adjusts timing of opening and closing of an intake and an exhaust valve depending upon an engine driving condition. More specifically, the invention relates to a valve timing control system having a simplified construction for easy installation for an automotive internal combustion engine.
2. Description of the Background Art
U.S. Pat. No. 4,231,330 discloses a variable valve timing control system for an automotive internal combustion engine. In the disclosed system, a camshaft for controlling timing of opening and closing of an intake and an exhaust valve is engaged with a sleeve at its front end through thread engagement. A valve timing control mechanism includes an outer cylinder carrying a timing sprocket drivingly associated with an output shaft of the engine via a timing chain or timing belt for rotation in synchronism therewith. The outer cylinder is formed with an internal gear teeth. The internal gear teeth is engaged with an external gear teeth of a cylindrical timing adjusting element which has an internal gear teeth engaging with the external gear teeth of the camshaft. One of the external and internal gear teeth of the timing adjusting element is formed into a helical gear. The timing adjusting element is hydraulically or mechanically driven in axial direction depending upon the engine driving condition for causing relative angular offset of the camshaft with respect to the timing sprocket. By this, relative rotational phases of the camshaft and the sprocket can be offset for causing variation of the valve opening and closing timings.
As set forth, the prior proposed valve timing control system takes a strategy of establishing direct engagement of the timing adjusting element with the external gear teeth of the camshaft. During assembling process, meshing of the timing adjusting element and the external teeth of the camshaft is down simultaneously of installation of the sleeve onto the front end of the camshaft by means of fastening bolts. Such construction includes shortcoming in difficulty of adjustment of the relative angular position of the camshaft and the timing sprocket. Namely, in the prior proposed system, adjustment of relative angular positions of the camshaft and the timing sprocket has to be done after installation of the sleeve onto the camshaft. This requires special adjusting tool or device for satisfactorily adjust the initial phase relation between the camshaft and the sprocket. As a result, production process becomes substantially complicate and costful.